Method for improving the data transmission quality in data packet oriented communication networks

ABSTRACT

The transmission quality of a first data stream, in particular a real time data stream, which competes with at least one further data stream for a restricted transmission capacity at a network node in a data packet oriented communication network, is improved by increasing the data rate of the first data stream by adding redundant data at the transmitter end. During an overload situation, the increase in the data rate of the first data stream in comparison to that of the at least one further data stream overrides the latter to the extent that a greater proportion of the jointly available transmission capacity at the network node is now taken up by the first data stream.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of copending InternationalApplication No. PCT/DE00/03680, filed Oct. 19, 2000, which designatedthe United States.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

[0002] The invention lies in the communications field. Morespecifically, the invention relates to a method for improving the datatransmission quality in data packet oriented communication networks,that is, for improving the transmission quality of a first data streamthat is to be transmitted from a transmitter via a network node in adata packet oriented communication network to a receiver. The datastream has a predetermined data rate and it is to be passed on from thenetwork node together with at least one further data stream. If thetransmission capacity which is jointly available for the data streams isexceeded, data packets in the data streams to be transmitted arerejected by the network node.

[0003] In data packet oriented communication networks, also referred toas packet-switched communications networks, data streams to betransmitted are split into individual data packets, which are providedwith a destination address and are transmitted via network nodes in thecommunication network to the respective transmission destination. Inthis case, the transmission process normally takes place withindifferent layers of transmission protocols, such as the IP protocol(Internet protocol) as a layer three protocol and the so-called TCPprotocol (transmission control protocol) or the so-called UDP protocol(user datagram protocol) as layer four protocols. The above numbering ofthe protocol layers relates to the so-called OSI reference model.

[0004] Data packets are frequently transmitted using a transmissionprotocol, such as the IP protocol, which does not guarantee correcttransmission for each individual data packet. For the purposes of atransmission protocol such as this, overload situations which occur in anetwork node or on a transmission path are coped with by rejecting thedata packets which initiate the overload situation, and thus by nottransmitting them any further. The transmission destination normallyuses a higher-level transmission protocol, such as the TCP protocol, torequest the transmitter of the data packets to repeat the transmissionof data packets which do not arrive at the transmission destination forthis reason. However, such protection of data transmission is notsuitable for real time applications since the necessity to request adata packet once again creates major delays at the receiver inreconstructing the data stream of transmitted data without gaps.

[0005] When transmitting real time data, such as voice data or videodata, via a packet oriented communication network, the data rate of thereal time data is frequently reduced (in order to reduce the overload inthis way) in order to decrease the rate at which data packets are lostas a result of the overload. This is frequently done by using datacompression methods. However, compression of real time data improvestheir transmission quality in an overload situation only when theoverload situation is also predominantly caused by the transmission ofreal time data. If the overload situation is caused mainly by thetransmission of other data, compression of the real time dataessentially results only in the capability to transmit the other datamore quickly. Furthermore, when real time data, especially voice data orvideo data, are compressed, the information content of the real timedata is frequently not retained completely. As a result, the signalquality deteriorates, particularly in the case of voice data or videodata. Furthermore, the compression process delays the real time data toa relatively major extent, in particular in the case of transmission viadata packet oriented communication networks, since it takes acorrespondingly longer time to fill individual data packets withcompressed real time data.

SUMMARY OF THE INVENTION

[0006] It is accordingly an object of the invention to provide a methodfor improving the transmission quality of data to be transmitted via adata packet oriented communication network which overcomes theabove-mentioned disadvantages of the heretofore-known devices andmethods of this general type. With the foregoing and other objects inview there is provided, in accordance with the invention, a datatransmission method with improved transmission quality, the method whichcomprises:

[0007] transmitting a first data stream at a predetermined data ratefrom a transmitter via a network node in a data packet orientedcommunication network to a receiver;

[0008] forwarding data of the first data stream from the network nodetogether with data from at least one further data stream and, if atransmission capacity that is jointly available for the data streams isexceeded, rejecting data packets in the data streams to be transmittedby the network node;

[0009] adding redundant data to the first data stream with thetransmitter and thereby increasing a redundancy and increasing a datarate of the first data stream arriving at the network node in relationto a data rate of the at least one further data stream, and to therebycause a greater proportion of the jointly available transmissioncapacity to be taken up by the data of the first data stream.

[0010] The method according to the invention allows the transmissionquality of a data stream which is to be transmitted from a transmittervia a network node in a data packet oriented communication network to atransmitter to be improved considerably. This applies in particular topacket-switched transmission of real time data such as voice data and/orvideo data—also referred to as “Voice over IP” (VoIp) or “Video over IP”by the skilled artisans. The method according to the invention can beapplied to a large number of communication networks, such as so-calledlocal area networks (LAN) and wide area networks (WAN), using differenttransmission protocols, such as the Internet Protocol (IP), without anynecessity to intervene in the existing structure of the communicationnetworks. The transmitting network node may in this case be, forexample, a bridge which is also referred to as an L2 switch, a routerwhich is also referred to as an L3 switch, a so-called gateway or someother data packet switching device in the communication network.

[0011] Network nodes such as these normally reject data packets when thedata rate of the data streams to be transmitted exceeds the transmissioncapacity of the network node, or of its transmission lines. In anoverload situation such as this, a proportion of the data packets aregenerally rejected from all the data streams which are contributing tothe overload. For example, if the amount of data to be transmitted istwice the transmission capacity of a network node, every alternate datapacket from all the data streams which are contributing to the overloadis thus rejected by the network node.

[0012] On the basis of the method according to the invention forimproving the transmission quality of a first data stream, which iscompeting with at least one further data stream (which is to betransmitted via the network node) for a restricted transmission capacityat the network node or in one of its transmission lines, the data rateof the first data stream is increased by the transmitter addingredundant data. During an overload situation, the increase in the datarate of the first data stream in comparison to the data rate of the atleast one further data stream overrides the latter to the extent that agreater proportion of the jointly available transmission capacity istaken up by the first data stream. Once the data rate of the first datastream has been increased, assuming that the proportion of rejected datapackets remains the same, or increases slightly, this results in agreater proportion of data packets that are not rejected in the firstdata stream arriving at the receiver than before the increase. Theoriginal information content of the first data stream can thus bereconstructed better by the receiver, thus improving the transmissionquality.

[0013] The method according to the invention can be applied particularlyadvantageously to transmission of real time or quasi real time data at apredetermined data rate, since there is no need for any additional delayto the data to be transmitted. The method can be used particularlyadvantageously in local area networks, wherein no charges are incurredby increasing the data rate of a data stream to be transmitted.

[0014] The method according to the invention makes it possible toallocate a greater proportion of the transmission capacity of a networknode to a data stream which is to be transmitted via that network node.In this context, it is particularly advantageous that there is no needfor any intervention in existing communication networks or networknodes.

[0015] The redundancy of the first data stream can be increased in manyways, for example by adding parity information, checksums, and/orredundant data using the so-called CRC method (cyclic redundancy check).According to one particularly simple embodiment variant, the data ratecan be increased by copying the data packets in the transmitter. Oneadvantage of this embodiment variant is that there is normally also noneed to make any changes to the receiver to carry out the methodaccording to the invention, since the data packet transmission protocolswhich are normally used generally provide correct handling of datapackets which arrive more than once. Apart from increasing the datapacket rate, the data rate of the first data stream can also beincreased by lengthening its data packets. This is particularlyadvantageous when the transmission capacity is restricted less by thedata rate than by the data packet rate in the network node.

[0016] In accordance with an added feature of the invention, thereceiver can determine a measure for the transmission quality of thefirst data stream. A measure such as this is represented, for example,by the proportion of data packets that are not received from the firstdata stream. This proportion can be determined, for example, by usingthe so-called RTP protocol (real time transport protocol) to number thedata packets in the original first data stream. An acknowledgement canthen be transmitted from the receiver to the transmitter, preferablyusing the so-called RTCP protocol (real time control protocol) dependingon the determined measure for the transmission quality. Theacknowledgement can be produced, for example, whenever the transmissionquality falls below a predetermined limit.

[0017] Such monitoring and acknowledgement of the transmission qualityis already provided as standard in the RTCP protocol, so that a largenumber of existing communication devices with the RTCP protocolimplemented in them can be used unchanged as receivers for the purposesof the method according to the invention. The transmitter can use anacknowledgement received by it to add redundant data to the first datastream, depending on this acknowledgement. For example, on receiving anacknowledgement which indicates that only every alternate data packet inthe first data stream is arriving at the receiver, the data rate of thefirst data stream can be doubled by the transmitter by adding anappropriate amount of redundant data. The acknowledgement may alsocontain information, predetermined by the receiver, on the nature andamount of redundant data to be added to the first data stream by thetransmitter.

[0018] In accordance with a concomitant feature of the invention, thetransmitter can transmit to the receiver information about the redundantdata which it has added to the first data stream. This information may,for example, indicate the nature and amount of redundant data added. Theinformation content of the first data stream can then be reconstructedfrom the data packets received by the receiver using the transmittedinformation. By way of example, a reconstruction method matched to thenature of the redundant data (for example the CRC method) may be chosenusing the received information about the redundant data.

[0019] Other features which are considered as characteristic for theinvention are set forth in the appended claims.

[0020] Although the invention is illustrated and described herein asembodied in a method for improving the data transmission quality in datapacket oriented communication networks, it is nevertheless not intendedto be limited to the details shown, since various modifications andstructural changes may be made therein without departing from the spiritof the invention and within the scope and range of equivalents of theclaims.

[0021] The construction and method of operation of the invention,however, together with additional objects and advantages thereof will bebest understood from the following description of specific embodimentswhen read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a schematic block diagram of a communications system fortransmitting real time data and general data in a first transmissionmode; and

[0023]FIG. 2 is a schematic block diagram of the same communicationssystem in a second transmission mode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Referring now to the figures of the drawing in detail, each ofthe drawing figures shows, schematically, the same communication systemwith two terminals EG1 and EG2 for real time communication, for exampletwo video telephones. The system also has two data servers DS1 and DS2,as well as two network nodes NK1 and NK2, which are coupled to oneanother directly or indirectly, in a data packet oriented communicationnetwork. The communication network may in this case, for example, be inthe form of a local area network (LAN) whose LAN subnetworks areconnected by way of the network nodes NK1 and NK2, which are in the formof routers. In the present exemplary embodiment, the maximumtransmission capacity for data transmissions from the network node NK1to the network node NK2 is restricted to 10 Mbit/s.

[0025] The terminal EG1 and the data server DS1 are coupled to thenetwork node NK1, while the terminal EG2 and the data server DS2 arecoupled to the network node NK2. A data connection is set up between thedata server DS1 and the data server DS2, and a real time communicationconnection is set up between the terminal EG1 and the terminal EG2, viathe network nodes NK1 and NK2. While general data AD are transmitted bythe data server DS1 at a data rate of 19 Mbit/s for the purposes of thedata connection, real time data ED, for example voice data and/or videodata, must be transmitted at a data rate of 1 Mbit/s, which is governedby the real time requirements, for the purposes of the real timecommunication connection. Both the real time data ED and the generaldata AD are transmitted within data packets, which are each providedwith a destination address.

[0026]FIG. 1 shows a first transmission mode, wherein the real time dataED are transmitted as a first data stream at a data rate of 1 Mbit/s tothe network node NK1. In parallel with this, the general data AD aretransmitted as a second data stream at a data rate of 19 Mbit/s from thedata server DS1, likewise to the network node NK1. Since the maximumavailable transmission capacity for data transmissions from the networknode NK1 to the network node NK2 is only 10 Mbit/s, but the sum of thedata rates of the data streams to be transmitted is 20 Mbit/s, thenetwork node NK1 passes on only every other one of the available datapackets to the network node NK2. The other data packets are rejected.For the present exemplary embodiment, it is assumed that the networknode NK1 handles the data streams to be transmitted with equal priority,that is to say it rejects approximately the same proportion of datapackets from each data stream to be transmitted. This means onlyapproximately half the data packets from the real time data ED and fromthe general data AD are in each case delivered via the network node NK2to the respective transmission destination EG2 or DS2. A fragmentedstream of general data AD thus arrives at the data server DS2 at a datarate of approximately 9.5 Mbit/s, and a fragmented stream of real timedata at a data rate of approximately 0.5 Mbit/s arrives at the terminalEG2. While the data server DS2 can request the data server DS1 toretransmit the rejected data packets from the general data AD using ahigher-level transmission protocol, such as the TCP protocol, anyrequest for retransmission of rejected data packets from the real timedata ED would generally lead to an intolerable delay. If voice data isbeing transmitted as the real time data ED, although the transmittedspeech content generally remains comprehensible even when half the voicedata to be transmitted is lost, owing to the natural redundancy in voicedata, the transmission quality of the speech content is neverthelessconsiderably worse.

[0027] The terminal EG2 monitors the transmission quality of thereceived data stream of real time data ED by regularly determining theproportion of data packets which are not received. This proportion canpreferably be determined, using the RTC protocol, by numbering the datapackets in the first data stream transmitted by the terminal EG1. Then,depending on the determined transmission quality, the terminal EG2 sendsan acknowledgement RM, preferably in accordance with the RTCP protocol,back via the network nodes NK2 and NK1 to the terminal EG1. In thepresent exemplary embodiment, the acknowledgement RM contains theinformation that only half of all the data packets of the real time dataED have been received by the terminal EG2. Such an acknowledgement,relating to the transmission quality of received real time data, isalready normal in a large number of terminals which are used inconjunction with data packet oriented voice transmission (VoIP: voiceover IP).

[0028] After receiving the acknowledgement RM and evaluating it, theterminal EG1 changes to a second transmission mode, which is shown inFIG. 2. In this case, the terminal EG1 adds additional redundant data RDto the data stream of real time data ED, in order to increase theredundancy in this data stream, so that its data rate is increased. Thefactor by which the data rate is increased is in this case governed bythe proportion of data packets received by the terminal EG2, asindicated in the acknowledgement. Thus, in the present exemplaryembodiment, the data rate of the first data stream is doubled to 2Mbit/s by adding the redundant data RD. Additional information inaccordance with the CRC method may be added, for example, as redundantdata RD. The respective data contents of individual data packets withreal time data ED can preferably be distributed, together with theredundant data RD, over a number of data packets in the first datastream. According to one particularly simple variant, each individualdata packet of real time data ED can also be duplicated by the terminalEG1, and can thus be transmitted to the network node NK1 twice.

[0029] The sum of the data rates of the data streams transmitted to thenetwork node NK1 is now 21 Mbit/s, and thus exceeds the maximumtransmission capacity of the transmission path between the network nodesNK1 and NK2 by 2.1 times. Since, averaged over time, only 10 of 21 datapackets are thus passed on by the network node NK1, a data stream offragmented general data AD arrives at the data server DS2 at a data rateof approximately 9 Mbit/s, and a fragmented data stream, comprising thereal time data ED and the redundant data RD, arrives at the terminal EG2at a data rate of approximately 1 Mbit/s. While the data rate of thereceived general data AD for the data server DS2 is reduced onlyslightly, the data rate of the data received by the terminal EG2 isapproximately doubled. Since the data rate of the fragmented transmitteddata stream comprising real time data and redundant data correspondsapproximately to the data rate of the real time data ED originally to betransmitted, the terminal EG2 can reconstruct this real time data ED toa very great extent using the transmitted redundant data RD. Thetransmission quality of the real time data ED is thus improvedconsiderably.

[0030] The method according to the invention thus makes it possible, ina simple way and without any changes being required to existingcommunication networks or their network nodes, to use the transmissionquality to regulate a so-called quality of service parameter (QoS) for adata packet oriented connection. Since it is generally assumed that thetransmission volume of non-real-time data will rise to a major extent inthe future in comparison with the transmission volume of real-time data,one may quite confidently presume that increasing the data rate for realtime transmissions using the method according to the invention will betolerable, or will have a rather negligible effect.

[0031] If the terminal EG2 finds that the transmission quality of thereceived data stream has improved, that is to say a smaller proportionof data packets are being rejected, then the terminal EG2 can transmit afurther acknowledgement to the terminal EG1, in order to cause the datarate to be reduced by reducing the proportion of redundant data added.

[0032] Furthermore, the terminal EG2 can check whether the transmissionquality of the real-time data ED is being improved effectively as aresult of an increase to the data rate of the data stream transmitted bythe terminal EG1. If no predetermined improvement occurs, a furtheracknowledgement can be transmitted to the terminal EG1 in order in thisway to cause the terminal EG1 to cancel the increase in the data rateonce again. This reduces the load on the communication network.

I claim:
 1. A data transmission method with improved transmissionquality, the method which comprises: transmitting a first data stream ata predetermined data rate from a transmitter via a network node in adata packet oriented communication network to a receiver; forwardingdata of the first data stream from the network node together with datafrom at least one further data stream and, if a transmission capacitythat is jointly available for the data streams is exceeded, rejectingdata packets in the data streams to be transmitted by the network node;adding redundant data to the first data stream with the transmitter andthereby increasing a redundancy and increasing a data rate of the firstdata stream arriving at the network node in relation to a data rate ofthe at least one further data stream, and to thereby cause a greaterproportion of the jointly available transmission capacity to be taken upby the data of the first data stream.
 2. The method according to claim1, which comprises increasing a data packet rate for the first datastream by the transmitter for additional transmission of the redundantdata.
 3. The method according to claim 2, wherein the adding stepcomprises producing copies of data packets in the first data stream toform redundant data, for transmission to the network node.
 4. The methodaccording to claim 1, which comprises increasing a length of datapackets in the first data stream by the transmitter for additionaltransmission of the redundant data.
 5. The method according to claim 1,which comprises distributing, with the transmitter, data contents of adata packet to be transmitted in the first data stream, together withredundant data, over a number of data packets that are transmitted fromthe transmitter to the network node.
 6. The method according to claim 1,which comprises: determining, in the receiver, from the first datastream a measure for a transmission quality thereof; transmitting withthe receiver an acknowledgement to the transmitter depending on thedetermined measure for the transmission quality; and adding redundantdata to the first data stream with the transmitter depending on theacknowledgement.
 7. The method according to claim 6, which comprisesreducing a data rate of the added redundant data by the transmitter ifno predetermined improvement in the transmission quality is found. 8.The method according to claim 1, which comprises adding redundant datato the first data stream by the transmitter on request by the receiver.9. The method according to claim 1, which comprises transmittinginformation about the redundant data from the transmitter to thereceiver; and at least partially reconstructing, in the receiver, aninformation content of the first data stream from the data packetsreceived by the receiver in the first data stream, depending on thetransmitted information.
 10. The method according to claim 1, whichcomprises transmitting quasi real time data within the first datastream.
 11. In a data transmission method of the type in which a firstdata stream of a given data rate is transmitted in a data packetoriented communication network from a transmitter, via a network node,to a receiver, and the first data stream is to be passed on from thenetwork node together with at least one further data stream, andwherein, if a transmission capacity that is jointly available for thedata streams is exceeded, the network node rejects data packets in thedata streams to be transmitted, the improvement which comprises: addingredundant data to the first data stream to thereby increase a redundancyand to increase a data rate of the first data stream arriving at thenetwork node relative to a data rate of the at least one further datastream, and to thereby take up a greater proportion of the jointlyavailable transmission capacity with data of the first data streamrelative to data of the at least one further data stream and to therebyimprove a transmission quality of the first data stream.